Recent three-dimensional simulations of core-collapse
supernovae have revealed the existence of non-axisymmetric
modes of the Spherical Accretion Shock Instability, or SASI.
Here we investigate the growth of these modes using
two-dimensional simulations of the accretion flow in the
equatorial plane of a core-collapse supernova. By perturbing
a steady-state model we are able to excite both one- and
two-armed spiral modes that grow exponentially with time,
demonstrating that these are linearly unstable modes. By
tracking the distribution of angular momentum, we
demonstrate that these modes are able to efficiently
separate the angular momentum of the accretion flow (which
maintains a net angular momentum of zero), leading to a
gradual spin-up of the underlying accreting proto-neutron
star.

This work was performed under the auspices of the TeraScale
Supernova Initiative, funded by SciDAC grants from the DOE
Office of Science High-Energy, Nuclear, and Advanced
Scientific Computing Research Programs.